Apparatus for removing zinc particle deposits from an electrode

ABSTRACT

The invention provides an apparatus for removing zinc particle deposits from substantially the entire face of a major surface of an electrode in an electrochemical bath, the apparatus comprising a plate attached to actuating means for affecting relative movement between the plate and the major surface of the electrode, the plate being provided with a scraper blade-retaining slot along one of its edges, and further comprising a scraper blade removably inter-engaged with the slot, the blade extending from the slot towards the surface of the electrode, and extending substantially along the entire length of the major surface of the electrode, the actuating means being arranged to move the scraper from a first position to a second position in a first downward stroke to affect scraping of individual zinc particle deposits from substantially the entire face of the major surface of an adjacent electrode and then to return the blade from the second position to the first position in a second upward stroke.

The present specification is a continuation in part of U.S. patentapplication Ser. No. 08/314,764 filed Sep. 29th, 1994, now U.S. Pat. No.5,565,083, which was a continuation in part of U.S. patent applicationSer. No. 08/088,543, filed Jul. 6, 1993, now U.S. Pat. No. 5,378,329which, in turn, was a continuation in part of U.S. patent applicationSer. No. 07/636,411, filed Dec. 31, 1990, now U.S. Pat. No. 5,228,958.

The present invention relates to an apparatus for removing zinc particledeposits from a major surface of an electrode in an electrochemicalbath.

More particularly, the present invention relates to an apparatus forremoving zinc particle deposits from substantially the entire face of amajor surface of an electrode in an electrochemical bath for use in aprocess for the preparation and/or regeneration of an alkaline-zincslurry utilizable in rechargeable zinc batteries, such as zinc-airbatteries, and especially for the preparation and/or regeneration of analkaline-zinc slurry utilizable in rechargeable electric batteriesintended for use in electric vehicles.

BACKGROUND OF THE INVENTION

Various proposals have been made in the past for electric-poweredvehicles. To date, for a number of reasons, electric vehicle systemshave yet to become generally commercially viable for urban and highwayapplications. There have been proposals to employ zinc-air batteries forurban vehicle propulsion. An example is the publication "Improved SlurryZinc-Air Systems as Batteries for Urban Vehicle Propulsion," by P. C.Foller, Journal of Applied Electrochemistry, Vol. 16, pp. 527-543(1986).

Metal-air battery structures are described in the followingpublications: U.S. Pat. No. 4,842,963, entitled "Zinc Electrode andRechargeable Zinc-Air Battery;" U.S. Pat. No. 4,147,839, entitled"Electrochemical Cell with Stirred Slurry," U.S. Pat. No. 4,908,281,entitled "Metal-Air Battery with Recirculating Electrolyte;" U.S. Pat.No. 3,847,671, entitled "Hydraulically-Refuelable Metal-Gas DepolarizedBattery System;" U.S. Pat. No. 4,925,744, entitled "Primary Aluminum-AirBattery;" U.S. Pat. No. 3,716,413, entitled "RechargeableElectrochemical Power Supply;" U.S. Pat. No. 4,925,744, entitled"Primary Aluminum-Air Battery."

In U.S. Pat. No. 3,592,698, entitled "Metal Fuel Battery with FuelSuspended in Electrolyte," there is described inter alia a method forcirculating an electrolyte/metal fuel powder mixture through batteries;U.S. Pat. No. 4,126,733, entitled "Electrochemical Generator Comprisingan Electrode in the Form of a Suspension" relates to a similar subject,using a circulated suspension of inert cores coated with anelectrochemically active material. In U.S. Pat. No. 4,341,847, entitled"Electrochemical Zinc-Oxygen Cell," there is described a method in whichan electrolyte is circulated in the annular space between concentricelectrodes.

Electrical energy storage systems are described in the followingpublications: U.S. Pat. No. 4,843,251, entitled "Energy Storage andSupply Battery with Recirculating Electrolyte;" "Energy on Call" by JohnA. Casazza, et al., IEEE Spectgrum, June 1976, pp. 44-47; U.S. Pat. No.4,275,310, entitled "Peak Power Generation;" U.S. Pat. No. 4,124,805,entitled "Pollution-Free Power Generating and Peak Power Load ShavingSystem;" U.S. Pat. No. 4,797,566, entitled "Energy Storing Apparatus."

Regeneration of spent zinc-containing alkaline electrolyte is describedin a number of prior patents. For example, in U.S. Pat. No. 3,847,671(mentioned above), whole spent electrolyte is subjected to electrolysis,when zinc deposited at the cathode is removed with a wiper blade. Thethus-removed zinc is the to be substantially heavier than theelectrolyte (35-40% KOH) and hence falls to the bottom of each cell. Ina particular embodiment, the cathode and anode are specified as beingmade from copper (or silver-plated copper) and carbon, respectively. InU.S. Pat. No. 3,981,747, it is proposed to regenerate the spent zinc inan alkaline electrolyte by reaction with a strongly electropositivemetal, such as magnesium or aluminum, which displaces the zinc. In U.S.Pat. No. 4,341,847 (also mentioned above), spent zinc in the alkalineelectrolyte is regenerated either by reversing the current and platingzinc on the anode, or by mechanically replacing zinc oxide particles byactive zinc particles.

Moreover, it is of importance in batteries containing zinc electrodesthat the zinc should not be consumed by a reaction with aqueouselectrolyte, especially alkaline electrolyte which generates hydrogengas, which reaction merely corrodes the zinc and prevents itsavailability for producing electric current. A number of prior patentsrelate to this problem.

Thus, e.g., in U.S. Pat. No. 4,112,205, double salts containing bothmercuric and quaternary ammonium ions are used as inhibitors in galvaniccells comprising zinc anodes, notably in Leclanche-type batteries,containing ammonium chloride/zinc chloride electrolyte; U.S. Pat. No.3,945,849 employs quaternary ammonium halides as inhibitor for zincanodes in similar primary cells. U.S. Pat. No. 4,195,120 teachesalkaline cells containing a predominantly zinc anode and, as a hydrogenevolution inhibitor, a surfactant which is an organic phosphate ester ofthe ethylene oxide adduct type. Metal oxide inhibitors for zinc (inpractice ZnO) electrodes are described in U.S. Pat. No. 4,084,047, inwhich the inhibitors are mixed thoroughly with the ZnO; the inhibitorstaught in this patent are binary combinations of oxides which excludemercuric oxide, the latter being regarded as an ecologicallyunsatisfactory additive for the ZnO electrode. According to U.S. Pat.No. 4,084,047, it was known to mix or alloy the active zinc in zinc-zincoxide anodes and their supporting grid (e.g., copper or silverstructures) with 0.5-5.0 wt. % mercury or mercuric oxide.

It will also be appreciated by persons skilled in the art thatamalgamation of zinc with mercury has been known for a very long time,and that it is carried out in neutral or more usually, in acid solution,e.g., by reacting zinc with mercury chloride in dilute hydrochloricacid.

In U.S. Pat. No. 5,228,958, there is described and claimed a process forthe regeneration of an at least partially-spent slurry having adissolved phase and an undissolved phase for use in metal-air batteries.

In U.S. Pat. No. 5,232,798 there is described and claimed a method forthe inhibition of corrosion in particulate zinc.

The disclosures of all of the foregoing publications (includingpatents), including also the prior art described therein, are explicitlyincorporated herein by reference.

It is an object of the present invention to make possible, from apractical point of view, the general commercial viability ofzinc-alkaline batteries, more particularly zinc-air batteries, for usein electric vehicle propulsion and energy storage systems. A morespecific object of the invention is to provide a process for preparing azinc slurry for zinc-alkaline cells and/or regenerating a rechargeableslurry for use in zinc-air batteries. Such a slurry would be applicable,for example, in a mechanically refuelable zinc-air battery in which,following discharge, the spent zinc is replaced with regenerated zincfor the subsequent discharge.

One of the major problems which required solution to make theregeneration process commercially feasible is an effective way forremoving deposits from a major surface of an electrode in anelectrochemical bath.

More particularly, the process described and claimed in co-pending U.S.Ser. No. 08/088,543 inter alia comprises electrolyzing an admixturecontaining zinc, which has been at least partly oxidized, to anoxidation product selected from the group consisting of zinc oxide, zinchydroxide and zincates in a cell with a corrosion-resistant anode and anon-zinc-adherent cathode such that the zinc which deposits on saidcathode self-detaches or is removable by a method selected frombrushing, scraping, vibrating, the use of liquid jets, either fixed ormoving, and the use of electrical pulsing, until no more than apre-selected amount of zinc remain in the solution. However, the methoddescribed in said application was that the cathode was transferred to aseparate container every ten minutes, where the deposited zinc wasremoved by scraping with a plastic spatula and homogenized into aparticulate structure by means of a revolving nylon brush, while a cleancathode was placed in the electrolytic bath to continue the zincrecovery process.

While such a method indeed works, it is not practical for massregeneration of thousands of anodes for the cells of electric fuelbatteries.

As mentioned hereinbefore, U.S. Pat. No. 3,847,671 relates to ahydraulically referable metal-gas depolarized battery system which interalia purports to teach an electrode arrangement as described in column9, lines 25-32 as follows:

Wipers 66 extend the height of each electrode and are wiped across theface of each negative electrode to remove the spongy zinc deposittherefrom as fast as it forms, thereby making room for more depositwithout filing the cell. The dislodged powder is removed from the bottomof each cell periodically to a manifold (not shown), from which it ispumped into slurry tank 48.

An examination of FIG. 5 of said patent reveals that wipers 66 are infact vertical triangular prisms, with one apex serving to movehorizontally back and forth across the electrode surface.

The problem with such a configuration, however, is that it has now beenfound that the wedge shape of the prism directs liquid in said bathtowards the line of contact between the scraper and the electrode,whereby the resulting hydrodynamic forces work against an effectivescraping contact and action.

SUMMARY OF THE INVENTION

With this state of the art in mind, there is now provided according tothe present invention a apparatus for removing zinc particle depositsfrom substantially the entire face of a major surface of an electrode inan electrochemical bath, said apparatus comprising a plate attached toactuating means for affecting relative movement between said plate andsaid major surface of said electrode, said plate being provided with ascraper blade-retaining slot along one of its edges, and furthercomprising a scraper blade removably inter-engaged with said slot, saidblade extending from said slot towards said surface of said electrode,and extending substantially along the entire length of the major surfaceof said electrode, said actuating means being arranged to move saidscraper from a first position to a second position in a first downwardstroke to affect scraping of individual zinc particle deposits fromsubstantially the entire face of said major surface of an adjacentelectrode and then to return said blade from said second position tosaid first position in a second upward stroke.

It is to be noted that it is possible to make the scraper plate andscraper blade in one piece. However, there are economic advantages inmaking the plate out of a rigid but low-cost plastic, such aspolypropylene while the blade is made of an abrasion-resistant but moreexpensive material such as polysulfone.

When, as in the present invention, the scraper plate and blade are madeseparately and then assembled, very little space can be allocated forattachment hardware, such as fasteners. The scraper must operate in thenarrow space available between the anode and the cathode. Such space isnarrow due to design considerations such as reducing electrical lossesduring electrowinning. The present invention provides several solutionsto this problem.

In preferred embodiments of the present invention, said blade isflexible and is moved from a first position to a second position by saidactuating means in a first stroke to affect scraping of individual zincparticle deposits from substantially the entire face of said majorsurface of said electrode, and in which said blade is further urgedtowards said surface of said electrode by hydrodynamic forces exerted bysaid liquid in said bath and is returned from said second position tosaid first position by said actuating means in a return stroke in whichsaid blade is urged away from said surface by hydrodynamic forcesexerted by said liquid in said bath.

The invention also provides a scraper for removing deposits from a majorsurface of an electrode in an electrochemical bath, comprising a plateattached to actuating means for affecting relative movement between saidplate and said major surface of said electrode, said plate beingprovided with a scraper blade-retaining slot along one of its edges,said slot being angled relative to the plane of said plate with itsopening extending towards said electrode surface and further comprisinga scraper blade provided with means for removable inter-engagement withsaid slot.

In a first preferred embodiment of the present invention said slot isprovided with a plurality of spaced-apart pins extending betweeninterfacing inner walls of said slot and said scraper blade comprises afirst edge provided with a plurality of spaced-apart keyhole slots,sized and spaced to override said pins when said edge is inserted insaid slot, and having an opposing second edge for scraping deposits fromsaid electrode.

Preferably each plate is made of an inexpensive plastic suitable for usein a KOH solution at temperatures up to 90° C., such as polypropylene ora fluoroplastic. The plate has large through-going apertures to allowionic conductivity between the anode and the cathode.

The blade is made of a plastic with high mechanical strength, such aspolysulfone.

With regard to the angle between the plate and the blade, if this is toolarge, too little shear force is applied to the zinc particles which areto be removed. On the other hand, too small an angle will require ablade that is too long and weak. In the present invention this angle isbetween 7d and 25d.

In U.S. Pat. No. 4,417,953 there is described a process for separatingan electrolytic deposit from both sides of a a generally verticallysuspended cathode comprising detaching at least a portion of the upperedge of each deposit from its respective side of the cathode, attachinga set of suction cups to each deposit, moving said sets of suction cupsin a first step to an intermediate position, in which the depositsattached to the sets of suction-cups are in a form of a substantiallyV-shaped-configuration so that deposits are separated off the cathodedownwardly, and bringing in a second step the sets of suction cups fromsaid intermediate position to a rest position in which the sets ofsuction cups are oriented so that the deposits attached thereto arepositioned beneath them, as well as an apparatus and a system foreffecting the same. Said patent also describes and claims the use ofknives for separating said deposits from the cathode so that they can begripped by said suction cups. However, as can be noted from FIG. 8 ofsaid patent and the description therein, e.g. in column 5, lines 16-18and column 6, lines 43 and 44, said knives are attached to a pivot andserve to widen the gap between the deposits 9 and the cathode 1 bypeeling the deposited layer away from the cathode so that it can begripped by said suction cups.

Similarly, U.S. Pat. No. 3,625,806 describes a machine for stripping offa copper coating from a basic plate, which machine includes one or tworeciprocating knives to remove continuous pieces of sheet metal fromsaid basic plate.

As will be realized, both of these patents are directed to knives whichscrape only a narrow path roughly as wide as the knife itself, in orderto detach a continuous plate which can be as wide as the active area ofthe cathode, since prying pressure exerted along any surface of such adeposited plate between said plates and the electrode on which it isdeposited is sufficient to peel the entire plate away from saidelectrode.

In contradistinction, the present invention is directed to the use of ascraper blade similar in function to a windshield wiper, which iseffective for scraping of individual zinc particle deposits fromsubstantially the entire face of an electrode on which they aredeposited, even though said deposits are not continuous or connected toeach other and therefore must be individually acted upon.

In an especially preferred embodiment of the present invention, there isprovided a process for the preparation of an alkaline-zinc slurry foruse in batteries, said slurry comprising an admixture of zinc which hasbeen at least partly oxidized to an oxidation product selected from thegroup consisting of zinc oxide, zinc hydroxide and zincates; an aqueoussolution consisting essentially of potassium hydroxide and potassiumzincate; and an inorganic or organic inhibitor, effective to inhibit theinteraction of zinc and potassium hydroxide in aqueous solution, whichwould otherwise result in the evolution of hydrogen gas; said processcomprising the steps of electrolyzing said admixture in a cell with acorrosion-resistant anode and a non-zinc-adherent cathode such that thezinc which deposits on said cathode is removable by scraping until nomore than a preselected amount of zinc remains in the solution, providedthat the current density at the cathode is preselected so that inconjunction with the non-zinc-adherent characteristic of the cathode,the electrowon zinc will have, after homogenizing into particles, adensity within the range of 0.2-2.0 g/cc and a surface area within therange of 0.5-6.0 m² /g; removing zinc from the cathode utilizing ascraper comprising a plate attached to actuating means for affectingrelative movement between said plate and said major surface of saidelectrode, said plate being provided with a scraper blade-retaining slotalong one of its edges, said slot being angled relative to the plane ofsaid plate with its opening extending towards said electrode surface andsaid scraper further comprising a scraper blade provided with means forremovable inter-engagement with said slot, for scraping deposited zincfrom said cathode; collecting and homogenizing said scraped zinc intoparticles; combining said homogenized zinc particles with additionalaqueous potassium hydroxide and optionally with other makeup componentsselected from the group consisting of water and inhibitor to form acharged slurry; optionally analyzing said charged slurry in order toascertain whether at least the concentration values of zinc, thepotassium hydroxide and the inhibitor lie within preset limits; andoptionally adjusting the concentration values of at least one of saidaforementioned zinc, potassium hydroxide or inhibitor to within presetlimits for said charged slurry.

The invention will now be described in connection with certain preferredembodiments with reference to the following illustrative figures so thatit may be more fully understood.

With specific reference now to the figures in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

IN THE DRAWINGS:

FIG. 1 is a perspective view of a preferred embodiment of the scraper,the bath being sectioned, according to the invention;

FIG. 2a is a detail end-view of a second embodiment;

FIG. 2b is a sectional view taken along AA of FIG. 2a;

FIG. 3 is a fragmented sectional view of a third embodiment;

FIG. 4 and 5 are end views of an embodiment using hydrodynamic forces tocontact and separate the scraper blade and the electrode; and

FIG. 5 is a fragmented end view of a fourth embodiment.

There is seen in FIG. 1 a scraper 10 for removing deposits 12 from amajor surface 14 of an electrode 16 in an electrochemical bath 18. Forsimplicity the drawing shows a single electrode 16 and scraper 10. In apractical arrangement, large numbers of electrodes 16 are scraped inparallel formation, and facing each electrode 16 is a counter-electrodeof opposite polarity, and there is a scraper on each side of thecathode.

The scraper 10 comprises a plate 20 and an attached scraper blade 22.

Suitably the plate 20 may be made of polypropylene, which material hasoutstanding chemical resistance. It is, however, advantageous that theplate 20 be rigid, which can be achieved by using a plate 5-10 mm thick,or by using a ribbed plate.

Plate rigidity can also be achieved by using a nylon-covered steel. Theplate 20 is attached to actuating means 24 for affecting relativemovement between itself and the electrode 16.

The scraper plate 20 is advantageously provided with apertures 23allowing ionic conductivity between adjacent electrodes of oppositepolarity.

Actuating means 24 may comprise reciprocating pneumatic or hydrauliccylinders or a crank drive obtained from a slowly revolving shaft todrive the scrapers 10 in a vertical plane. In a further embodiment (notshown) the scrapers 10 are clamped and the bath 18 is driven toreciprocate in a vertical plane. All actuating means 24 mentioned arewell known and require no elaboration.

The plate 20 is provided with a scraper blade-retaining slot 26 alongone of the plate edges 28. The slot 26 is angled relative to the planeof the plate 20. The slot opening 30 extends towards the electrodesurface 14.

The scraper blade 22 is provided with means 32 for removableinter-engagement with the slot 26. In this embodiment means 32 comprisea roughened surface on the major surfaces of the scraper blade 22, whichis then held by friction in the tight-fitting slot 26.

The blade 22 is best made flexible so as to adapt itself to anyirregularities in the surface 14 with which it is in contact. It hasbeen found that a blade 22 of thickness between about 0.7 and 1 mmoperates very satisfactorily.

With regard to selecting a suitable material for the blade 22, metalsare unsuitable as there is the danger of causing a short circuit in thebath 20; they are also likely to receive an unwanted coating of zinc.Nevertheless, an abrasion-resistant material is required forsatisfactory scraping performance. It has been found that awell-operating blade 22 may be made of polysulfone. This is a strongpolymer which can also operate at elevated temperatures while retainingits dimensional stability.

Referring now to FIGS. 2a and 2b, there are seen details of a scraper 34which is similar to the scraper 10. However, the method of retaining theblade 36 in the blade-retaining slot 38 of the plate 40 is different.There are provided a plurality of spaced-apart pins 42 extending betweeninterfacing inner walls of the slot 38. The scraper blade 36 comprises afirst edge 44 provided with a plurality of spaced-apart keyhole-shapedslots 46, sized and spaced to override the pins 42 when the edge 44 isinserted in the slot 38. The blade 36 has an opposing second edge 48 forscraping deposits 12 from the electrode 16. In comparison with thescraper blade 22 of FIG. 1, the blade 36 is held more securely.

The blade 36 may conveniently be assembled to the plate 40 bytemporarily bending the blade 36 in a direction, causing opening of thekeyhole-shaped slots 46. On the release of the blade 36 in contact withthe pins 42, the slots 46 reassume their original dimensions to firmlyhold the blade 36.

FIG. 3 shows a scraper 50, similar to the scraper 10, though with adifferent retention means.

The blade-retention slot 52 provided in the plate 54 has a femaledovetail shape. The scraper blade 56 is provided with a matching maledovetail 58 near its first edge 60. The scraper blade 56 is furtherstabilized by contact with the lower edge 62 of the plate 54. The blade56 is oriented at an angle of between 7d and 25d from the plane of theplate 54.

The present invention also provides for two processes.

PROCESS A

In the following description, reference is again made to FIG. 1. Aprocess for removing deposits 12 from a major surface 14 of an electrode16 in an electrochemical liquid-containing bath 18. The processcomprises periodically moving a scraper 10 along a major surface 14 ofan electrode 16. The scraper 10 has been fully described with referenceto FIG. 1.

In a second embodiment of this process, the electrode 16 is a cathode,separated from an anode (not shown) by a distance of between 5 to 15 mm.The scraper 10 is built to have a total thickness of slightly less thanthis distance and operates satisfactorily in this confined volume.

In a third embodiment of this process the electrode 16 is a non-zincadherent cathode, and the deposits 12 are metal deposits of zinc.

Referring now to FIGS. 4 and 5, there is seen an apparatus 68 similar tothat seen in FIG. 1.

In a fourth embodiment of the process a blade 70 is moved from a firstposition, as seen in FIG. 5, to a second position, as seen in FIG. 4, byactuating means 24 in a first stroke to affect scraping of the electrode72. The blade 70 is further urged towards the electrode surface 14 byhydrodynamic forces exerted by liquid 74 in the bath 76. The blade 70 isreturned from the second position to the first position by the actuatingmeans 24, connected to a plate 80, in a return stroke in which the blade70 is urged away from the surface 14 by hydrodynamic forces, shown byarrows P, exerted by said liquid 74 in the bath 76, as seen in FIG. 5.

Scraping is thus carried out without the need for the provision of meansto press the scraper blade 70 against the surface 14. Furthermore, onthe return stroke when no scraping is carried out, unnecessary abrasionof the blade 70 is automatically prevented as the hydrodynamic forcescause separation of the blade 70 from the surface 14.

PROCESS B

A process for the preparation of an alkaline zinc slurry for use inbatteries.

The slurry comprises an admixture of:

a) zinc which has been partly oxidized to an oxidation product selectedfrom the group consisting of zinc oxide, zinc hydroxide and zincates;

b) an aqueous solution consisting essentially of potassium hydroxide andpotassium zincate; and

c) an inhibitor, effective to inhibit the interaction of zinc andpotassium hydroxide in aqueous solution, which would otherwise result inthe evolution of hydrogen.

The process comprises the following steps:

a) Electrolyzing said admixture in a cell with a corrosion-resistantanode and a non-zinc-adherent cathode, such that the zinc which depositson said cathode is removable by scraping until no more than apreselected amount of zinc remains in said aqueous solution, providedthat the current density at the cathode is preselected so that inconjunction with the non-zinc-adherent characteristic of the cathode,the electro-won zinc will have, after homogenizing into particles, adensity within the range of 0.2 to 2.0 g/cc and a surface area withinthe range 0.5 to 6.0 m² /g.

b) Removing zinc from the cathode utilizing a scraper 10, which has beenfully described with reference to FIG. 1.

c) Collecting and homogenizing said scraped zinc into particles.

d) Combining said particles with additional aqueous potassium hydroxideand optionally with other make-up components selected from the groupconsisting of water and inhibitor, to form a charged slurry.

e) Optionally analyzing said charged slurry in order to ascertainwhether at least the concentration values of zinc, the potassiumhydroxide and the inhibitor lie within present limits.

f) Optionally adjusting the concentration values of at least one of saidaforementioned zinc, potassium hydroxide or inhibitor to within presentlimits of said charged slurry.

FIG. 6 depicts a fourth embodiment of a scraper 82. The scraper plate 84is provided with an angled blade-retaining slot 86 along a lower edge 88of the plate 84. The slot 86 provides accommodation for the scraperblade 90 and also for a locking element 92 inserting along the length ofthe slot 86 and being in frictional contact with the blade 90 and theslot 86. An example of a suitable locking element 92 is a high-strengthnylon cord of the type used in fishing reels.

It will be evident to those skilled in the art that the invention is notlimited to the details of the foregoing illustrative embodiments, andthat the present invention may be embodied in other specific formswithout departing from the essential attributes thereof, and it istherefore desired that the present embodiments be considered in allrespects as illustrative and not restrictive, reference being made tothe appended claims, rather than to the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed is:
 1. An apparatus for removing zinc particle depositsfrom substantially the entire face of a major surface of an electrode inan electrochemical bath tank, said electrochemical bath tank includingan electrode at least partially immersed in an electrochemical solution,and said apparatus operating in conjunction therewith, comprising:aplate attached to actuating means for effecting relative movementbetween said plate and said major surface of said electrode, said platehaving a scraper blade-retaining slot along one of its edges, and ascraper blade removably inter-engaged with said slot, said slot fixablypositioning said blade relative to said plate, said blade extending fromsaid slot towards said surface of said electrode, and having a lengthsubstantially equalling the entire length of the major surface of saidelectrode, said actuating means moving said scraper blade from a firstposition to a second position in a first downward stroke to scrapeindividual zinc particle deposits from substantially the entire face ofsaid major surface of an adjacent electrode and then returning saidscraper blade from said second position to said first position in asecond upward stroke.
 2. An apparatus according to claim 1, wherein saidblade is flexible, is angled relative to a direction of said strokes andis moved from a first position to a second position by said actuatingmeans in a first stroke to effect scraping of individual zinc particledeposits from substantially the entire face of said major surfaces ofsaid electrode, and in which said blade is further urged towards saidsurface of said electrode by hydrodynamic forces exerted by saidsolution in said bath tank and is returned from said second position tosaid first position by said actuating means in a return stroke in whichsaid blade is urged away from said surface by hydrodynamic forcesexerted by said solution in said bath tank.
 3. An apparatus according toclaim 1, wherein a dovetail-shaped blade-retention slot is provided inone of said scraper plate and said scraper blade, and a matchingdovetail provided on the other of said scraper blade and said scraperplate, said slot and said matching dovetail securely and fixedly holdingand interengaging said plate and said blade when assembled in a requiredrelationship for scraping zinc particle deposits from said electrode. 4.An apparatus according to claim 1, wherein said plate is made ofpolypropylene.
 5. An apparatus according to claim 1, wherein said bladeis made of polysulfone.
 6. An apparatus according to claim 1, whereinthe thickness of said blade is between about 0.7 and 1.0 mm.
 7. Anapparatus according to claim 1, wherein said slot is oriented at anangle of between 7° and 25° from a plane of the plate.
 8. An apparatusaccording to claim 1, wherein said plate is rigid.
 9. An apparatusaccording to claim 1, wherein said plate is made of nylon-covered steel.